1. Field of the Invention
This invention relates to adhesion promoting organosiloxane compositions. More particularly, this invention relates to organosiloxane primer compositions that cohesively bond organosiloxane elastomers to organic polymers during curing of the elastomers by a hydrosilation reaction. The primer compositions do not contain the objectionable ingredients required in prior art compositions to achieve adhesion when the elastomers are cured at temperatures below about 80.degree. C.
2. Background Information
U.S. Pat. No. 4,719,262, which issued to Edwin Plueddemann on Jan. 12, 1988 describes primer compositions containing organosilicon compounds useful as primers. One group of organosilicon compounds described in this patent comprises bis-silylalkanes of the formula (--O).sub.3 SiRSi(O--).sub.3 where R represents an alkylene radical. Each of the silicon atoms is bonded to 1 or two alkoxy radicals and the remaining silicon-boarded groups are substituted or unsubstituted alkenyloxy, alkenyloxyalkoxy, or carbonalkenyloxyalkoxy groups, where the ethylenic unsaturation is located at terminal carbon atoms. This patent also teaches improving the performance of the disclosed organosilicon compounds as bonding agents by combining them with (A) copolymers derived from 1) ethylenically unsaturated organic compounds such as esters of acrylic and methacrylic acids, and 2) ethylenically unsaturated alkoxysilanes, and (B) organohydrogensiloxanes as crosslinking agents for the copolymer.
The copolymers referred to as A in the aforementioned patent are described in U.S. Pat. No. 3,306,800, which issued to Edwin Plueddemann on Feb. 26, 1967.
Primers and adhesion promoters containing the combination of the aforementioned ingredients A, B and the bissilylalkanes described in the Plueddemann U.S. Pat. No. 4,719,262 provide excellent adhesion between organosiloxane elastomers and amorphous organic polymers such as polymerized esters of acrylic or methacrylic acids, polycarbonates and polystyrene. Primer compositions containing these ingredients in combination with a solvent selected from ethylenically unsaturated alcohols containing from 4 to 6 carbon atoms are described in U.S. Pat. No. 4,795, 775, which issued on Jan. 3, 1989.
A disadvantage that may prevent wide acceptance of adhesion promoting compositions described in U.S. Pat. Nos. 4,795,775 and 4,719,262 is the toxicity of some organosilicon compounds containing the bis-silylalkyl group that can be present in these compositions. Organosilicon compounds containing the bis-silylethylene group .tbd.SiCH.sub.2 CH.sub.2 Si.tbd. are particularly undesireable. This disadvantage has stimulated a search for less toxic organosiloxane adhesion promoters suitable for use with organosiloxane elastomers that cure by a platinum catalyzed hydrosilation reaction.
Primer compositions containing various combinations of organosilicon compounds with alkyl orthosilicates and/or organohydrogensiloxanes are described in the prior art.
Coatings formed from (meth)acrylate polymers containing pendant alkoxysilyl groups are described in U.S. Pat. No. 4,491,650, which issued on Jan. 1, 1985. The polymers are prepared by reacting a poly(meth)acrylate containing pendant hydroxyl groups with an isocyanato-functional alkoxysilane.
Canadian Patent No. 2,069,564, which issued on Dec, 1, 1992 describes primer compositions containing an alkoxysilane that optionally contain a reactive organic group bonded to silicon, an organotitanate and a tin salt of a carboxylic acid.
Primer compositions containing an organotitanate in combination with either an organosilicon compound containing at least 2 silicon-bonded alkoxy groups or an organohydrogensiloxane that optionally contains silicon bonded alkoxy groups are described in U.S. Pat. No. 4,749,741.
Japanese Patent Publication No. 86/004865 describes primer compositions containing an organosilicon resin, an organohydrogensiloxane and an organotitanate.
Japanese Patent Publication No. 91/031266 describes a primer for the copier rolls of an electrostatic copier. The primer contains an organosilicon compound with alkenyl groups, an organohydrogensiloxane, a platinum-containing hydrosilation catalyst and an organotitanate.
One objective of this invention is to define a class of adhesion promoting compositions that will cohesively bond organic polymers to organosiloxane compositions that cure to form elastomers by a hydrosilation reaction while in contact with the organic polymer.